Designing for ultrahigh-temperature applications: The mechanical and thermal properties of HfB2, HfcX, HfNX and αHf(N)

• Published in: Journal of materials science Vol. 39; no. 19; pp. 5939 - 5949
• Main Authors: WUCHINA, E, OPEKA, M, CAUSEY, S, BUESKING, K, SPAIN, J, CULL, A, ROUTBORT, J, GUITIERREZ-MORA, F
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Heidelberg Springer 01.10.2004
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics; Structural ceramics; Technical ceramics; Thermal expansion; thermomechanical effects; Thermal expansion; thermomechanical effects and density; Thermal properties of condensed matter; Thermal properties of crystalline solids; Scanning electron microscopy; Brittle fracture; Hafnium boride; Mechanical properties; Plastic deformation; Experimental study; Solid solution; Modeling; Non oxide ceramics; Structural ceramic; Hafnium carbide; Reaction sintering; Young modulus; Thermal properties; Bending strength; Thermal expansion; Hot pressing; Hafnium nitride; Thermal conductivity; Manufacturing; Microstructure
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/B:JMSC.0000041690.06117.34

The thermal conductivity, thermal expansion, Young's Modulus, flexural strength, and brittle-plastic deformation transition temperature were determined for HfB2, HfC(0.98), HfC(0.67), and HfN(0.92) ceramics. The mechanical behavior of alpha-Hf(N) solid solutions was also studied. The thermal conductivity of modified HfB2 exceeded that of the other materials by a factor of 5 at room temperature and by a factor of 2.5 at 820DGC. The transition temperature of HfC exhibited a strong stoichiometry dependence, decreasing from 2200DGC for HfC(0.98) to 1100DGC for HfC(0.67) ceramics. The transition temperature of HfB2 was 1100DGC. Pure HfB2 was found to have a strength of 340 MPa in 4 point bending, that was constant from room temperature to 1600DGC, while a HfB2 + 10% HfC(x) had a higher room temperature bend strength of 440 MPa, but that dropped to 200 MPa at 1600DGC. The data generated by this effort was inputted into finite element models to predict material response in internally heated nozzle tests. The theoretical model required accurate material properties, realistic thermal boundary conditions, transient heat transfer analysis, and a good understanding of the displacement constraints. The results of the modeling suggest that HfB2 should survive the high thermal stresses generated during the nozzle test primarily because of its superior thermal conductivity. The comparison the theoretical failure calculations to the observed response in actual test conditions show quite good agreement implying that the behavior of the design is well understood.